A power consuming facility can include many interconnected pieces of electrical equipment that collectively and dynamically create a power system profile presented to the power utility providing the electrical power to the facility. Three key elements related to a power system profile are power quality, power efficiency, and power system performance. While similar considerations arise in regard to many other kinds of facilities, these elements are particularly important in regard to data processing facilities, since such facilities often impose a substantial electrical load on the utility power system. The load presented to a utility power system by a data processing facility and its resulting power system profile are generally undesirable because of the harmonic distortion and phase imbalance of the load, and because the load is not well managed, for example, in regard to meeting time-of-day, and peak demand power usage considerations of the utility.
There are several reasons why the power profile of a data processing facility tends to differ from that desired by a utility power system. Part of the problem arises because the engineering practices for designing and running a data processing facility at least partially fail to take into consideration the loads imposed by the power supplies of servers and other digital components installed in the facility. In practice, data system engineering and electrical power engineering have two disparate specialties with little in common, other than general interface information. Little or no standardization exists between the pieces of equipment in a data system and the power system that serves it. In addition, the management of the data processing equipment has generally been limited to manual control, which is ineffective in responding in real time to changes in the facility load or to changes in the quality of power being delivered to the data processing facility by the utility, or the demand on the power utility system. Again, however, it must be emphasized that this problem is not unique to data processing facilities, since many types of manufacturing and industrial facilities suffer from the same shortcomings in controlling the electrical load at the facility, and the quality of power characteristics of the load, to achieve a desired power profile.
As used herein, the term “facility” is any collection of electrical devices at a site that share a common power source—usually an electrical power utility. The following discussion is particularly relevant to facilities that include loads that can readily be controlled by a digital signal from a controller. Illustrations of such facilities include a network server farm, a building with computer, switch, and/or router equipment drawing power from the same electrical circuit, a group of residential living spaces, each of which has computers and other digital devices connected to a shared primary electrical utility circuit, and manufacturing and industrial sites with non-linear loads of this type.
A brief discussion of the manner in which electrical power is supplied by a power utility will help to better understand why managing the load at a facility can be important. Electrical power is generated at power plants, hydroelectric facilities, and by other means and conveyed from the generating sources over transmission lines at relatively high voltages (e.g., 60 kV and above) to reduce I2R losses. Transformers at substations located near the communities where the electrical power will be used reduce the voltage (e.g., to 2400 V or 12 kV) and convey the electrical power at these voltages over distribution lines, as three-phase power. Pole or pad-mounted distribution transformers further reduce the voltage, and the secondaries of these distribution transformers are connected to facilities that use the power.
The load on the utility power system is variable and tends to increase during the day when more power consuming devices are being used in industrial facilities, and as the result of ambient temperature changes that can increase the air conditioning load in buildings. Excessive loading on the power utility system circuits as a result of high air conditioning demand can reduce the voltage on the utility grid and cause “brown out” conditions, which correspond to lower voltages in the power provided to each facility connected to utility distribution circuits. To minimize such problems, utility companies give preference to customers who can manage the electrical load at their facilities to reduce the likelihood of excessive loading on the system when the demand peaks.
However, there are many short term transient effects and longer term effects besides peak demand that can directly impact the quality of the power being delivered to a facility by a utility company. Each time that a distribution switch opens or closes on a utility circuit, transient impulses can be generated that propagate throughout the power grid. Also, changes in loading and the quality of the load at one connected facility can impact the utility distribution circuit supplying power to the facility and thus, can adversely impact connected electrical loads at other facilities on that distribution circuit.
For example, if a facility imposes a substantial reactive load on a distribution circuit, due to a relatively large number of transformers or large motors being energized at the facility, a lagging power factor (shift of the phase angle between voltage and current) can result. Utilities generally prefer that the load imposed by each customer on a circuit be as close to unity power factor as possible. If necessary, capacitor banks may be installed by the utility company to compensate for reactive loads at a facility, but the facility owner may then be assessed a surcharge to offset the cost incurred by the utility for providing that solution. An inequality in the loading by a facility on the three-phase power provided by the utility company can cause lower voltage on the phase of the utility circuit with the higher load, than on the other two phases, which is clearly not desirable for other customers with facilities connected to that distribution circuit.
In the United States, the supply voltage provided a facility may be either three-phase or single phase and is typically a voltage in the range from 220 VAC to 600 VAC. This voltage is supplied to one or more breaker panels in a facility and distributed from the breaker panels to a plurality of circuits within the facility. The power system for a facility may include from one to many thousands of large single or three-phase circuits, as well as small single phase loads. These loads combine to produce an electrical profile for the facility. Electrical power engineers typically specify equipment and circuit requirements for a facility to meet legal limits, standards, and design requirements, including limits imposed by the rate structure of the power utility, based on the maximum anticipated electrical power load that will be connected to the utility. This approach may initially ensure that the expected load can be handled, but if the load later grows and exceeds the anticipated maximum, the problem can be expensive to correct. The typical data facility design does not provide a convenient mechanism to manage the connected load to meet the limits of a given design, or of the power available from the utility company on a circuit.
In addition, since the electrical loads in a facility are typically dynamic, their performance characteristics can change. These variable performance characteristics include resistance, capacitance, inductance, total power consumed, power factor, and total harmonic distortion (THD). The individual, independent changes of each connected load collectively result in changes in the total power profile for a facility that is seen by the utility power system, and which may be measured using conventional means. Managed responses to changes in such system characteristics is presently performed only by the manual intervention of facility operators at the level of the power system, if implemented by power engineers, or at a data processing facility, for example, by manually changing network operating conditions, if implemented by data engineers. Either solution is achieved at a relatively high cost and normally in an inefficient and undesirable manner.
Thus, the separation of the utility system providing power to a facility, on the one hand, and the control of the power consuming devices within a facility, on the other, has led to facility power systems that are uncoordinated, inefficient, and incapable of responding appropriately and expediently to the power requirements of the various connected electrical devices. No system presently exists to provide integrated automated management of a facility's power system profile as presented to a utility system, by the direct control of individual pieces of equipment within a facility using information systems embedded in the facility power system itself, and by taking advantage of loads that can be controlled in response to digital signals, such as digital devices. It would therefore be desirable to provide a method and system for controlling the power system profile of a facility having an electrical load with one or more (perhaps thousands) digitally-controlled devices. It would further be desirable to use system data, control capabilities, and feedback to establish and maintain a desired power system profile for an overall facility in response to changing power and load conditions and the requirements of the utility system. Also, it would be desirable to provide a method and system to achieve power system efficiencies autonomously and thereby improve the power efficiency of digital loads, reduce harmonic distortion and other undesirable power system characteristics produced by digital loads, and thereby save costs compared to manual power management and power conditioning that would otherwise be necessary to mitigate the undesirable power characteristics produced by uncoordinated digital devices within a facility.